Heretofore, heat-sensitive recording materials have been well known, in which colorless or pale-colored basic dyes and organic or inorganic color formers are brought into contact with each other by application of heat to produce recorded images by utilizing the color reaction therebetween.
Recent remarkable advances in heat-sensitive recording systems have permitted high-speed operation of all apparatus utilizing a thermal head, such as heat-sensitive facsimiles and heat-sensitive printers. For example, modern heat-sensitive facsimiles can transmit a printed page of A4 size paper (210.times.297 mm) in 20 seconds, and modern heat-sensitive printers can print 120 or more letters per second. With development of such high-speed facsimiles and printers, it is now required for heat-sensitive recording materials which are used in the high-speed facsimiles and printers to have a high recording sensitivity (dynamic recording characteristics), cause no static recording within a low temperature range (60.degree. C. to 70.degree. C.), and to cause no piling due to attachment of tailings.
Some conventional high sensitivity heat-sensitive recording materials are prepared using combinations of dyes, phenol compounds such as bisphenol A, and sensitizers such as stearic acid amide. In a recording layer of such high sensitivity heat-sensitive recording materials, the sensitizer and phenol compound are compounded in a proportion ranging between 2 and 5 per part by weight of the dye. These heat-sensitive recording materials, however, have disadvantages in that the so-called static recording within a low temperature range (60.degree. C. to 70.degree. C.) occurs as the recording sensitivity is increased, and the piling property is poor since a large amount of the sensitizer is added.
It has therefore been desired to develop heat-sensitive recording materials which are well-balanced in the quality thereof and are suitable for use in high-speed recording.